Consumer and food producer demands of flexible food packaging continue to evolve and become increasingly challenging. Consumers prefer an “easy open” or easy peel package that only requires only moderate strength to open the package and where the package opens in a clean and concise manner. In this manner, the package will not accidently open with normal handling but will open cleanly under hand force without use of special tear notches, scoring, perforations, or mechanical devices. Generally, seal forces less than about 1500 g/in (about 590 g/cm) are required for the food packaging to be considered an “easy open” package.
In a similar manner, many food producers prefer a package that has improved seal hermetics and product shelf life. Improved seal hermetics extend the shelf life of food products and help to keep moisture and air from entering the product space where the food is contained. Hermetic seals extend the shelf life of the food product and improve the consumer's experience.
To improve the hermetic properties of finished food packaging, laminations have been done with specialty sealant films that are usually blown and generally constitute metallocene-catalyzed linear low density polyethylene (m-LLDPE) or similar layers. Commonly, such films are greater than 1.3 mil (130 gauge or 32.5 μm) in thickness and are laminated to biaxially-oriented polypropylene (BOPP) or polyethylene terephthalate (PET) films. While such prior art films can provide desired hermetic properties, such films are disadvantageous as they are quite thick and require more materials and are, thus, not as desirable for economic and environmental sustainability reasons. Significant economic and environmental sustainability benefits would be achieved if a thinner extrusion coating layer could be used while still providing similar hermetic performance levels.
Other packaging solutions available in the prior art satisfy the desired hermeticity requirement or the desired easy peel requirement but not both at the same time. For example, cast polypropylene laminated to cast or blown polyethylene achieves hermetic seals but not easy peel. Conversely, a seal layer comprising polyethylene contaminated with polybutylene achieves easy peel but not hermeticity.
There is, therefore, a need in the food packaging industry for a heat-sealing film that combines easy open or easy peel characteristics and hermeticity and which at the same time is achieved by a one-step extrusion coating process. A reduction in steps can be achieved by use of an extrusion coating of m-LLDPE or linear-low density polyethylene (LLDPE) layers. This can open up opportunities and designs to a wider customer base as the final package construction can be reduced from a print web/barrier web/blown sealant with either extrusion or adhesive laminations between each web and replaced by a print web/extrusion coated barrier web. Due to the generally higher melt indices of extrusion coating polymers versus blown polymers, sealability can be improved due to the easier nature for flow of the extrusion coating polymer. This, in turn, gives an advantage in downgauging and improved economics/waste reduction.
Additionally, many consumers desire an easy open package that takes nominal force to open less than about 1500 g/in (about 590 g/cm). Generally, forces above this range are often too high for some users and require technologies such as laser scoring, perforations, tear notches, scissors, etc. for the consumer to open the package. As mentioned earlier, easy-peelable structures are not uncommon in the industry but generally require doping the sealant layer interface with a slightly incompatible component, which compromises hermeticity.